Wayne Rooney, pictured in training with Manchester United this week, injured his knee during England's recent victory over Egypt at Wembley. Photograph: Jason Cairnduff/Action Images

Sir Alex Ferguson promised a fully-committed, attacking performance from his side in tomorrow's Champions League first knock-out round second-leg against Milan, where they will be protecting a 3-2 advantage from the first meeting at San Siro.

They will be aided by the return of Wayne Rooney, who missed Saturday's 1-0 Premier League win over Wolverhampton Wanderers with a knee problem. But Ferguson confirmed that Wes Brown, who was injured in that game, will be out for four to six weeks.

"He is fit," Ferguson said of Rooney. "There is a rapid improvement from Saturday morning because on Friday evening I didn't think he had any chance. It's good news. He is a threat to anyone at the moment."

Ferguson insisted that his side would not simply seek to defend the advantage gained in the first leg. "We're going to play our normal game and that includes attacking and always has," he said. "I don't think we should be confused by the 3-2. It's a very difficult game for us, and we'll treat it as such. We're hoping to kill the tie by our own attacking abilities but Milan have to score, which should make it a more open match."

Ferguson also suggested he was disappointed to win the first leg by just a single goal, after Clarence Seedorf scored for Milan with five minutes remaining. "The first 15 minutes was the good spell for them and the bad spell for us," he said. "Once we recovered we played very well and should maybe have killed the match in the second half."

Ferguson did not specify the nature of Brown's injury, but the full-back was known to have hurt his foot after a challenge with the Wolves midfielder Matt Jarvis, and left Molineux wearing a protective boot. There have been rumours that the England international had suffered a broken metatarsal.

The four-to-six-week timescale is at least good news for England, with Brown widely expected to be part of Fabio Capello's squad for the World Cup after playing at right-back against Egypt last week.

"Unfortunately, his career has been blighted with injury," said Ferguson. "He has got another one and will be out for four to six weeks but I hope I can get him back for some of the season."

In addition to Brown, Anderson (knee), Ryan Giggs (arm) and John O'Shea (leg) are also out of tomorrow's game.